I'd really love to just slide the episode forward in time slightly, so that we could find a month in the 30s that fits with all the data & clears up those anachronisms. Unfortunately, it's pretty definitely 1930, according to several lines Spock has in the episode. I have the book with Ellison's original script and introduction, and nowhere does he mention that it was ever planned as a two-parter. What's your source on that? And I doubt that the Condor subplot directly inspired "Mirror, Mirror." Other than the basic concept of an evil crew on the standing Enterprise sets, they don't really have much of anything in common. The Condor plot is pretty undeveloped in Ellison's script, as it was reportedly added at Roddenberry's demand that the ship be in danger in some fashion. And don't forget that "Mirror, Mirror" writer Jerome Bixby had already written several short stories about alternate universes.